Circuit breaker-balanced armature



April 29, 1947- H. c. GRAVES, JR 2,419,892

C IRCUIT BREAKER-BALANCED ARMATURE Filed Oct. 12, 1943 4 Sheets-Sheet l g=621NVENTu BY WWA ATFORNEY.

April 29, 1947- H. c. GRAVES', JR 2,419,892

CIRCUIT BREAKER-BALANCED ARMATURE Filed Oct. l2, 1943 4 Sheets-Sheet 2 pril 29, 1947. H. c. GRAVES, JR 2,419,892

CIRCUIT BR-EAKER-BALANCED ARMATURE Filed oct. 12, 1943 4 Sheets-Sheet 5 `nvm/wok. BY t I w Wl April 29, 1947.

H. C. GRAVES, JR

CIRCUIT BREAKER-BALANCED ARMATURE Filed OC..

4 Sheets-SheefI 4 INVENTOR.

Patented Aprl`29, 1947 CIRCUIT BREAKER-BALANCED ARMATURE Herbert C. Graves, Jr., West Chester, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application October 12, 1943, Serial No. 505,896

'z claims. 1

My present invention relates to circuit interrupters, and more particularly to the overcurrent feature thereof which is intended to be responsive to predetermined currents of selected intensity and duration automatically to trip the circuit breaker.

More specifically, my invention relates to a novel means for balancing the armature of the overcurrent feature of circuit breakers so that the armature will be unresponsive to sharp physical shocks of short duration Without interfering with its responsiveness to overcurrents of selected intensity and duration.

My invention contemplates that the armature of the overcurrent feature of the circuit breaker be balanced in all respects around its pivot point so that the moment of inertia on either side will be exactly the same.

The problem of balancing an armature in this manner becomes greatly complicated when timedelay elements are added to the'armature- While the armature itself may be prefectly balanced, the time-delay element secured to one side thereof necessarily tends to counteract or destroy this balance owing to the weight of the time delay sucker disc and the members which connect the same to the armature.

According, my invention contemplates not only the exact balancing of the armature itself, but also the provision of means for balancing the additional load of the time-relay sucker disc so that a true dynamically balanced condition may exist.

Since the time-delay sucker disc is restricted in its manner of travel by .the dashpot in which it rides, my invention also contemplates that the means utilized for balancing the weight of the time-delay sucker disc be likewise restricted in the path which it may follow so that a balanced condition may be obtained at every position of theY armature--at least up to the time it reaches the tripping position.

Thus, instead of a mere balance which may steadily and progressively be destroyed by the shifting of the weights with respect to their distance from a fulcrum, my armature may be balanced to such an extent that at every position thereof the load on either side of the pivot point will be exactly the same.

A primary object therefore of my invention is the provision of means for balancing a rotating armature of an overcurrent feature so that all parts thereof and attachments thereto are at all times perfectly counterbalanced in every position of the armature.

Such balancing of the armature is useful and indeed necessary wherever circuit breakers are to be used in installations which are subject to extremely rapid movements or physical shock conditions.

Thus. in naval combat vessels, the effect of a broadside or of the impact of gun fire or of a near miss of an aerial bomb may be such as to transmit a physical shock of tremendous intensity through the hull of the ship from the point of initial impact of the shock to any structure including circuit breakers which are secured to .the hull of the ship.

The type of shock here contemplated is not the mere heeling, skidding, or turning of the vessel itself, but the shock transmitted by a wave motion through the metallic hull of the ship at a speed of approximately 16,000 feet per second and which is thus impacted on the circuit breaker structure itself long before the vessel begins to move as a Whole in response to the overall effect of the shock.

Since the pivot pin of the armature ls secured -to some stationary portion of the circuit breaker which, in turn, is necessarily secured to some portion of the vessel, the pivot pin receives the impact of this shock and transmits it to .the armature. 1

Should the armature be in any degree unbalanced, this shock will initiate its rotation; and should the armature be balanced in only one position but on movement to another position become unbalanced, vibration may perhaps occur whereupon the physical shock will be impacted on the armature in itsV unbalanced position and will then be effective -to rotate it sufliciently to trip the circuit breaker.

But, when the armature and yall of its elements and attachments are constantly balanced in every position thereof, then the impact on .the pivot pin transmitted to the armature will be transmitted equally on either side of the pivot pin, and the armature will, by its own balanced condition, be prevented from rotating falsely.

The structure is so arranged that the tripping of the circuit breaker in response to an overcurrent of predetermined intensity and duration will will at that time create an unbalanced condition Accordingly, still a further object of my invention is the provision of a statically balanced armature which will be unresponsive to physical shocks of momentary duration but which will be responsive to a sustained pull owing to the energization of a magnet in the event of an overcurrent or short circuit condition.

In addition to balancing the armature by means of equalizing the moment of rotation of all the elements and attachments on either side of the armature, the armature may be balanced as efficiently by the use of balancing springs which oppose each other and which are free to adjust each other to equal tension or compression.

Another object oi my invention, therefore, is the provision of means for balancing an armature by means of opposing forces (such as springs) which are free to adjust themselves to equalize each other at all positions of the armature.

Still another and important feature of my invention is the arrangement of a time-delay element in connection with my armature where the.

armature may automatically be in effect disconnected therefrom in the event of excessive overcurrents or short circuits.

My invention contemplates the attachment of a time-delay sucker disc and dashpot to the overcurrent armature in such a manner that in the event of overcurrents of relatively low intensity, the time-delay will be effective to permit the circuit breaker to trip only if the low intensity overcurrent condition persists for a predetermined period of time.

My time-delay feature is, however, so connected to the armature that in the event of an excessive overcurrent condition, the armature may respond instantaneously and thus be automatically disconnected from the time-delay device.

For this purpose, a specific object of my invention includes the provision of a spring mem-- ber between the sucker disc of the time-delay device and the armaturethe said spring being so arranged that it will act essentially as a rigid structure in the event of overcurrents of relatively low intensity, but so that it wiil act as a structure the length of which may be changed (i. e., by compression) inthe event of excessive overcurrents or oi' short circuits.

These and many other objects of my invention will become apparent in the following description and drawings in which:

Figure i is a cross-sectional view of a typical circuit breaker in the closed position showing my improved balanced overcurrent feature mounted therein.

Figure 2 is a view corresponding to that of Figure i with portions of the circuit breaker of Figure 1 removed showing the overcurrent feature attracted to the tripped position and the circuit breaker open.

Figure 3 is a view partly in vertical cross section of the overcurrent feature of Figure 1 showing the same in the at-rest or unattracted position.

Figure 3a is a View corresponding to that of Figure 3 showing the arrangement of the parts in the event of a greatly excessive overcurrent or short circuit.

Figure 4 is a View similar to that of Figure 3 showing the position of the'overcurrent feature when attracted to the tripped position of Figure 2.

.of Figure 5 in response to shock.

Figure 7 is a view corresponding to those of Figures 5 and 6 showing the condition of the trip unit in response to an overcurrent condition.

In Figures 1 and 2 I have shown rather schematically a type of circuit breaker with respect to which my balanced overcurrent feature may advantageously be used. This circuit breaker is more fully described in my application Ser. No. 384,245, now Patent No. 2,338,715, dated January 11, 1944, and also in application Ser. No. 339,687 of William M. Scott, Jr., filed June 10, 1940, now Patent No. 2,348,223, dated May 9, 1944.

A brief preliminary description of the circuit breaker itself will aid in the understanding of the operation of the overcurrent feature.

The circuit breaker parts are mounted on an ebony asbestos panel I Il. Current enters through an upper back connection stud II, which passes through an opening in the panel I0 and which is secured to the panel I0 by means of the angle member I 2, the bolt I3, and the bolt I4, which latter bolt passes through the panel I0 and engages the terminal block I5 of the blow-out coil I3.

Current passes from the back-connection stud Il to the main stationary contact member 2|! and simultaneously through the blow-out coil I3 to the arcing horn ZI and thence to the stationary arcing contact 22. Current from the main stationary contact 20 passes to the main movablel contact 25 mounted on the movable contact carrying arm 26 which in turn is mounted on the shaft 21. Current then flows from the main movable contact 25 through the pigtail 30 to the terminal block 32 which is secured on the panel III by neans of the bolt 3I.

From the terminal block 32 current then passes through the overcurrent magnet 35 to the i, iower baci: connection stud 3E which is secured to the panel III in the same manner as is upper back connection stud il.

From the arcing horn 2l and the arcing contact 22, current passes through the movable arcing contact 4U to the pigtail 4I, then to the terminal block 32, and likewise through the overcurrent magnet 35 to the lower baci; connection stud 3S.

The shaft 2l, which operates the movable arfing and main contacts, is provided with a crank 45 to which is secured, -by means of pin 4B, the link 41 of insulating material which, in turn, may be moved up or down by means of the operating mechanism contained in the housing 50.

When the circuit breaker is tripped from the position of Figure to the position of Figure 2, the link 41, which has been supported in the housing 50, is permitted to drop, and the shaft 21 rotates in response to any suitable spring bias applied thereto, thus moving the contact elements to the position shown in Figure 2, whereupon current from the movable arcing contact Is transferred to the arcing horn 52 of the arc extinguisher 53.

'I'he current path through the arc thus drawn is maintained by the pigtail 54 between the arcing horn 52 and the lower terminal block 32. The arc is then blown out and extinguished by means of a blow-out coil I8 and the arc extinguisher I3.

All the various elements of the circuit breaker 5 above indicated are described more specically ln the applications above mentioned and thus rei quire no further description here.

It is suilicient to note, however, for purposes of the present description that the lever 80 is secured to a latch member contained in the housing 50, and when this lever 60 is lifted slightly, the latch trips and the circuit breaker may move from the closed position of Figure 1 to the open position of Figure 2.

The overcurrent feature 10, more specifically described in connection with Figures 3 and 4, is designed to lift the lever 60 in response to overcurrent conditions of predetermined intensity and duration.

As will be seen from a comparison of Figures l and 2, the armature is shown in the unattracted untripped position of Figure 1, and in the fully attracted tripped position of Figure 2.

The overcurrent feature 10 with the armature |00 and the overcurrent magnet 35 constitute the essential elements of my present invention and are more specifically shown in Figures 3 and 4 where it will be seen that the armature |00 is rotatably mounted on pin l0| supported in the housing |02 of the overcurrent feature 10.

The arm |03 of the armature |00 on the right side of the pin |0| (with respect to Figure 3) is provided with a tapped hole in the bridging member |05 through which is threaded the adjustable screw |04. Screw |04 is held in its adjusted position by the lock nut |06 and the spring washer |01.

When the armature |00 is attracted from the position of Figure 3 to the position of Figure 4, screw |04 strikes the lever 60 and lifts the same in order to trip the circuit breaker. It will be obvious, therefore, that screw |04 is adjusted so that the lever will be contacted substantially just before the armature |00 reaches the fully tripped position of Figure 4, so that the additional movement between the point of contact of screw |04 with the lever 60 to the completed movement of Figure 4 will be just sufficient to lift the lever 60 to the predetermined extent necessary to effect the tripping operation.

The overcurrent magnet 35 and the coil 31, which energizes the same, have a form wellknown in the art and need no further description.

Likewise, the elements |08, |00 and ||0 of the arm |03 of armature |00, which are attracted by magnet 35, are also of'a form well-known in the art and require no further description.

It is suiiicient to note for purposes of the present description that when magnet 35 is energized to a sufficient extent to overcome the inertia of the armature |00 and the time-delay mechanism herein described and the adjusting spring ||1, the elements |08, |09 and 0 of the arm |03 of the armature |00 are attracted by the magnet 35, and thus the screw I 04 is brought into contact with the lever 60 to trip the circuit breaker.

A bracket member 2 is secured to the arm |03 of the armature |00 in any suitable manner as, for instance, by the rivets ||3 and is provided with an extension ||4 having an opening 5 within which one end ||6 of the tension spring |1 is captured. 4

The opposite end ||8 of tension spring ||1 is secured to the extension 9 of the slide member |20.

Slide member |20 has a pair of flanges |2| and |22 which are provided with threaded openings 6 and are in screw-threaded arrangement with the adjusting screw |23.

Adjusting screw 231s rotatably mounted in openings |24 and |25 in the top wall |28 and the bottom Wall |21 respectively oi' the housing |02. The lower end of the screw |23 is provided with an extension |30 passing through and registering with the opening |25. The upper end of the screw |23 just beneath the undersurface of the top Wall |26 of the housing |02 is provided with a. pin |3| passing through the screw in registry with the groove |32 in the undersurface of the top wall |26 of the housing |02.

The tension of spring ||1 pulling between the extension ||9 of the slide member |20 and the extension i4 of the armature |00 pulls the screw |23 upwardly so that the pin |3| is caused to bear in the groove |32--this prevents false rotation of the screw |23 in response to jars or shocks which occur during tripping or owing to any other physical cause.

The front wall |35 of the housing |02 isprovided with a slot |36 through which projects the adjustng knob |31 of insulating material secured to the screw |23 and rotatable therewith. In order to rotate the screw |23 to adjust the position of the slide member |20, it is necessary to depress the adjusting knob |31 and rotate the same. Depressing the knob will Apull the pin |3| out of the groove |32 and make it possible to rotate the screw |23.

At each turn, the pin 3| will snap into the groove |32 once more so that the knob |31 must be depressed again to continue the rotation; or if a substantial turn is desired, the knob |31 must be continuously depressed during rotation.

As the screw |23 is thus manually rotated, the slide member |20 will move up or down in accordance with the direction of rotation of screw |23 to adjust the tension of the spring ||1.

The ilange member 2| of the slide |20 projects through the slot |36, and an appropriate scale may be mounted alongside the slot |36 so that the extension |2| of the slide may act as a i pointer to indicate the adjustment for which the spring I1 is set.

The arm |40 of the armature |00 on the left side of the pin |0| (with respect to Figure 3) is provided with a weight |42 secured thereto in any suitable manner, preferably by means of the rivets |43. This weight is designed to cooperate with the extension |40 ofthe armature |00 to counterbalance all of the members of the extension |03 of the armature. |00 on the right side of the pivot |0| so that the armature |00 is accurately balanced.

The adjustment of the spring l|1 determines the intensity of energization of the magnet 35 necessary to attract the armature |00 to effect' the tripping. The pull exerted by this spring is for obvious reasons not counterbalanced; since, if it were, the armature |00 would be sensitive to current no matter how minute; and since the tension of the spring |1'is unaltered by physical shock.

Since, by means of the Weight |42, section |40 of the armature |00 on the left side of pin |0| is exactly equa1 in weight and mass to section |03 of the armature |00 on the right side of pin |0|, any shock transmitted from the hull of the vessel to the pin |0| will be transmitted equally on either side of the pin |0| to equal masses on each side.

Should the force exerted by pin 0| be in an upward direction, then the side |40 and the side |03 ci.' the armature |00 will tend to move upwardly with equal moment, and the armature will, therefore, not rotate about the pin |0| this is obviously so since the armature |00 as a whole is a single rigid unit and both sides thereof cannot move upwardly simultaneously, unless it should break at the pivot pin l0 I Assuming for the moment that the armature |00 were not counterbalanced in the manner herein described, and the pivot pin l0| should transmit a shock in an upward direction, the armature |00 would rotate clockwise. This may result in a rebound with suilcient force to trip the circuit breaker, depending, of course, on the relationship between the force of the shock and the resistance oiered by the dash-pot.

Consequently, the balancing of the armature 00 in the manner herein described creates a condition which resists downward movement as well as upward movement of the armature |00 owing te physical shock transmitted thereto by the pivot pin 30|, and the armature 00 will not trip in that event either. The armature, indeed, es will be obvious, is balanced with respect to shock transmitted thereto in any direction.

It is well-known in the operation of circuit breakers that the energization of the tripping magnet 35 may vary within rather wide limits without effecting a tripping of the circuit breaker.

Thus, assuming that the circuit breaker is to operate on 60G volts, 100 amperes, it may be desired that the circuit breaker be adjusted so that it will trip the currents in excess of, say, 150 amperes.

bviously, of course, the attraction exerted on the armature i613 by the magnet 35 varies in ac-I cordance with the amount of current passing therethrough. Consequently, it may be argued froma theoretical point of view that ii the system be adjusted for operation at a particular current value, that an unbalanced condition may perhaps be obtained at different current values.

This, however, is not so. Since the attraction ci the magnet 35 and the tension of the spring lil are without mass and are therefore not afected by shock forces, they will maintain their relative tensions and the tripping point will not be altered.

En balancing7 the armature |00, it is therefore necessary to consider only the moving parts attached to it that have mass, and it is not necessary to consider those forces exerted on the armature |00 that do not have any mass since they will not be affected by shock and therefore will not tend to overbalance the armature |00.

One other source of unbalanced force under shock conditions, is the contact between the moving dash pot disc i| and the stationary disc |54. But, since these discs are immersed in oil and adhere to each other with a force greater than the shock forces, they may be neglected as a. cause of tripping under shock conditions. y

in the present invention, it is desired for practical operation to cause the armature |00 to trip not merely on a current of predetermined intensity. but only where this current is maintained over a predetermined time interval. For this purpose, it is necessary to provide a time-delay mechanism.

En the present case, the time-delay mechanism, shown in the dashpot |50, is secured in any suitable manner to the underside of the housing |02 and the sucker disc 15|, which is secured to the arm |03 of the armature |00.

The dashpot |50 comprises a chamber |53,

8 which is preferably nlled with oil, md is provided with a steel plate |54 secured adjacent to the bottom of the dashpot chamber |53 by means of the screw |55 passing through the opening |55 of the steel plate |54 and entering the tapped opening |51 and metal insert |58 in the base of the dashpot chamber.

The head of the screw |55 is recessed beneath the upper surface of the steel plate |54 to provide a relatively small depression or chamber |55 in the center of the upper surface of steel plate |54.

The sucker disc |5| is made preferably of steel with a central section |62 also of steel material.

A collar |63 is secured in any suitable manner as, for instance, by brazing to the upper surface of the sucker disc |5|; and the end |84 of connecting link |65 is secured in the collar |53.

The lower end of the connecting link |55 is threaded at |66 and is secured in the tapped opening of the tubular member |58. Tubular member |68 is provided with a flange |59 which bears against the lower outside surface of the tubular member |10.

The upper end of the connecting link |65 is also threaded at |12 and passes through the nut |13 in the tube |10.

A compression spring ||14 is mounted in the tube |10 between the base thereof and the underside of nut |13, and thus forces the nut |13 upwardly to force the flange'l59 of the tubular member |68 against the bottom of the spring tube |10.

A set screw |16 passes diametrically through the nut |13 and bears against the threaded end |12 of the connecting link |65 to maintain the adjustment of the nut |13.

The set screw |16 passes through slot |80 in the side of tube |10 and may be removed therethrough in order to permit rotation of the nut |13 to adjust the compression of the spring |14. In the event such adjustment is desirable, the set screw may be removed; the nut may then be rotated to the appropriate adjustment; and the set screw |16 may then be replaced to maintain the adjustment.

The upper end of the spring tube |10 is connegted by means of the pin |83 to the armature The spring tube |10 is guided in its upper and downward movement by a tubular insert |85 in the top of the housing of the dashpot |50.

This resilient interconnection between the sucker disc i5| and the armature |00 may be utilized for the purpose of making the armature |00 instantaneous on overcurrent values above a predetermined intensity.

Thus assuming, for instance, that the circuit breaker is to protect a circuit carrying 600 volts, amperes, and that it is intended to trip with a time-delay, should the current rise to smperes, and assuming further that it is intended to trip instantaneously when the current value reaches 1000 amperes-then, the adjustment of the spring |14 of the dashpot mechanism together with the adjustment of spring ||1 may be made to effect these various results.

The spring ||1 should, in the rst instance, in this case be adjusted so that it will resist the attraction of the armature |00 at any current value below 150 amperes but will permit the magnet 35 to be effective to attract the armature |00 above 150 amperes.

The spring |14 sh'ould be adjusted so that a force exerted by the magnet 35 on the armature |00 below 1000 amperes will be substantially ineffective to compress the spring |14; while a force exerted thereon by the magnet I6, owing to a. current in excess of 1000 amperes. will be sumcient to compress the spring |14.

Assuming, in this example, that an overcurrent should exist of more than 150 amperes, but less than 1000 amperes, then thefspring ||1 will no longer resist the attraction on the armature but the magnetic attraction, owing to a current of this value, will not be sufcient to compress the spring |14.

Accordingly, the connection from the amature |00 to the time-delay sucker disc |6| in this lcase is substantially rigid, and a time-delay will be eiected by the sucker disc |5| holding back the amature |00.

Thus, for an overcurrent value of between 150 amperes and 1000 amperes in this example, the sucker disc |5| will be effective to create the predetermined time-delay for which the dashpot |50 is set.

In the event that the current value, according to our example, should rise above 1000 amperes Where an instantaneous trip becomes desirable, then, by reason oi the adjustment of the spring above pointed out, this spring will be compressible, and the spring tube |10 will be enabled immediately to rise and compress the spring |14 against nut |13, and the armature |00 which is secured to the tube alone and without substantial movement of the dashpot disc |5|, will be able to rise as shown in Figure 3A.

In this case, the force exerted by the magnet 35 on the armature |00 will enable the tube |10, which is attach'ed to the armature |00, to compress the spring |14 instantaneously.

Since the tube |10 in turn is connected to the connecting link I 65, only through the spring |14, the fact that the connecting link |65 is held down by the sucker disc |5| will not affect the instantaneous operation of the armature |00 in response to an overcurrent of sufficient intensity to compress the spring |14.

The slot |80 in the side of the tube |10 Which permits the set screw |16 to pass through should, accordingly, he suiliciently long not only to allow for adjustment of the compression of the spring I 14, but also to allow the tube |10 to move with respect to the set screw and nut.

By this means, therefore, a dual overcurrent feature is obtained.

On relatively small overcurrents of relatively long duration, the circuit breaker will be en abled to trip only after the predetermined timedelay for which the dashpot |50 is set.

On substantial overcurrents or on short' circuits, the circuit breaker will be able to trip instantaneously irrespective of the setting of the dashpot |50.

In order to maintain the dynamic balancing feature of the armature |00 and its consequent resistance to shock it is necessary not merely to counterbalance each of the elements oi.' the armature itself, as above pointed out, but also to counterbalance the weight of the tube |10 and the elements associated therewith', as well as the connecting link |65 and the sucker disc |5|-all of which are secured to the right hand side of the armature |00.

These elements, it is obvious, are not integrated with the armature |00 so that they maintain the same relative position with respect to the pivot point |0| of the armature |00 as do the elements mounted on the armature itself; but they are pivotally mounted on the armature |00 and,

while adding to the weight of the right-hand side thereof, assume diilerent positions with respect to the other elements oi.' the armature as the armature |00 moves from one position to another.

Accordingly, the counterbalancing means should likewise preferably be pivotally mounted to assume similar angular positions.

For this purpose, an additional weight is pivotally hung on the pin |9| on the lefthand side of the pivot point |0| (with respect to Figure 3), and this weight 90 is added to by an additional Weight |92 secured on the pin |93 at the lower end of the Weight |90.

A link |94 is rotatably secured to the pin |93, and the opposite end is secured to the pin |95 carried by an extension |96 from the flange |91 secured to the underside of the housing |02.

The portion of link |94 supported by the pin |93. the additional weight |92, and the weight |90 are equally massed to the tube |10 and its associated elements; to wit, the nut |13, the spring |14, the connecting link |65, the tube |68, and the sucker disc |5I.

Accordingly, all of the additional elements hung from the right side of the pivot l0| of the armature |00 are counterbalanced by eie-l ments of the same mass hung in the same inanner from the left side of the armature |00. The continuous balancing of the armature |00 is maintained by this additional counterbalancing means.

In addition, it is obvious that the counterbalancing masses |90, |92 and |94 are maintained as far as possible in the same relative position with respect to the pivot pin |0| as are the tube |10 and other associated elements which they counterbalance.

In effect, the elements of the armature |00 and Weights defined by pins |0|, |9I, |93 and |96 form a quadrature linkage or parallelogram, the sides of which always remain equal and the elements of which counterbalance,the approximately parallelogram structure being defined by pins |0|, |83 and the extension |66 of the link |65 and the sucker disc |5|.

By means of the structures herein described,

the overcurrent feature is not only rendered stable with respect to physical shocks, but .is also so arranged that it may selectively respond in different ways to overcurrents of different intensities and durations.

rlhus, as above pointed out, the shock from the pin |0| or from any other element in contact with the armature |00 is transmitted equally on both sides of the armature owing to the equal masses on each side.

Since the opposite sides of the armature |00 both tend to rotate in the same direction (up or down) on opposite sides of the pivot pin lili, such a shock is translated into counterbalancing forces on opposite sides of the pivot pin, thus leaving the armature i 00 stationary irrespective of the intensity of the shock.

Also, as above pointed out, the overcurrent feature is so arranged that where the overcurrent is of relatively loW intensity, the timedelay element will be effective so that tripping will occur only if the lower intensity overcurrent condition lasts for a predetermined length of time.

Where-however, the overcurrent is of a predetermined greater intensity, then the armature |00 may trip instantaneously and is, in effect, automatically disconnected on the occurrence of such a condition from the time-delay element.

In Figures 5, 6, and 7 I have shown a further modiiication of my invention wherein the balancing of the armature is obtained by the use of counterbalancing springs. The embodiment is here shown schematically, but the development of this embodiment into commercial form should be obvious to those skilled in the art.

The armature 20@ in this embodiment is arranged pivotally mounted on the pin 20! and has a right-hand extension 203 and a left-hand section 240 preferably of equal mass. 20E, in the event of overcurrent conditions, may be attracted by the magnet 35.

Extension 283 of the armature is captured between the two rods 2li) and 2li, each of which is provided with a head 2i 2 and 2i3 respectively bearing against opposite sides of the arm 203 of the armature 205-.

The rods 2i@ and 2li are each supported rcspectively from the upper and lower walls oi" the flanges 2i5 and die of any suitable housing in which the element herein described may be enclosed.

The rods 2|@ and 2li' pass through suitable openings in each of the flanges 225 and 2l6 respectively and are each provided with washers 2 i8 and 2l?) respectively limiting the inward movement of the said rods toward the armature 203.

Any suitable means, as, for instance, the cotter pins 220 and 22i, may be utilized to prevent the rods 2 I 0 and 2i l from being unintentionally withm drawn from their mountings.

Compression springs 222 and 223 are mounted respectively on each of the rods 210 and 2i i and are in each case captured between the heads of the rods and the flanges or walls in which they are mounted.

In the event of the occurrence of a shock tending to effect rotation of the armature 200, it will be clear that with the opposite sides of the armature equally balanced, such rotation, owing to shock, will always be resisted by the occurrence or' equal forces in the same direction on opposite sides of the pivot pin 20 i.

In the event, however, that sufiicient wear should occur to slightly unbalance the opposite sides of the armature 200 with respect to each other, and in the event of a combination of physical shocks tending to eiect rotation 0f the armature 200 so that the end 240 moves upwardly and the end 203 downwardly, then, as will be seen in Figure 6, spring 2H will be compressed and ,wiliact as a shock absorber to absorb the rotative movement of the armature 200.

In the event of a combination of shocks and other circumstances which tend to produce a counterclockwise rotation of armature 200, then the upper spring 2|0 will be effective to absorb this rotation.

In the event, however, that the magnet 35 is energized sufficiently to attract the armature 200 to trip the circuit breaker, then, as shown in Figure 7, the end 203 of the armature 200 will strike the head 2I3 of the pin 2li to move the same The armature i 12 tween short, sharp physical shocks and a steady pull exerted by magnet Il'.

In the event oi such a short, sharp physical shock, the springs 223 or 222 will rebound to restore the armature 200 to its initial position irom that, for instance, of Figure 6 to that of Figure 5.

In the event of a steady pull exerted by the magnet 3-5', the spring 223 will be steadily compressed to result in the tripping operation as shown in Figure 7.

Suitable adjustment springs may be provided in connection with the armature 200 to ensure its response to overcurrents of predetermined intensity. It is possible, however, to avoid the necessity for additional adjustment springs since spring 223 can act as such an adjustment spring in the embodiments shown in Figures 5, 6 and The spring 223 is simply set initially for a predetermined adjustment.

However, the flange member or supporting; members 2 l5 and 2 IS may be made verticali; a instable in order to obtain an adjustmen4 spring 223-or the springs 222 and 223 me made adjustable in any other suitable mar Similarly, suitable time-delay elements, a.. viously` pointed out, may be secured to the ture 208 and may be counterbalanced m the manner previously pointed out.

tion only in connection with specific pretence embodiments thereof. Many variations and modifications should be obvious to those skilled in the art. Accordingly, I prefer to be bound not by the specific disclosures herein but only by the appended claims.

I claim:

l, In combination, a magnet winding, a pivoted armature rotated about its pivot in response to the energization of said magnet winding, said armature being mechanically balanced at all positions thereof about its rotating pivot, a time delay mechanism pivotally connected on one side of. the pivot of said armature for extending the time of operation of said armature in response to a predetermined energization of said magnet winding and a weight pivotally connected to the other side of the pivot of said armature and balancing said time delay mechanism, the connection of the weight being such that balance is affected at all positions of said armature.

2. In combination, a magnet winding, a pivoted balanced armature rotated about its pivot in response to the energization of said magnet winding, and a time delay mechanism connected on one side of the pivot of said armature for extending the time of operation of said armature in response to a. predetermined energization oi said magnet winding, a counter-balance means connected on the opposite side of the pivot of said armature and maintaining the same relative position with respect to the armature pivot for each position of the armature as said time delay mechanism maintains, whereby said armature and time delay mechanism are balanced at all positions of said armature against vibrations.

3. In combination, a magnet winding, a pivoted armature rotated about its pivot in response to the energization of said magnet winding, a mass connected to one side of the pivot of said armature and a time delay mechanism secured to said armature on the other side of its point of pivot, the said iirst mass and the mass of said time delay mechanism being balanced with respect to each other on both sides of said pivot, and means for so connecting said mass and time 13 delay mechanism that they maintain the same relative positions with respect to said armature pivot for all positions of said armature.

4. In combination, a magnet winding, a pivoted armature rotated about its pivot in response to the energization of said magnetwinding, and a time delay mechanism pivotally secured to said armature on one side of its point of pivot, the mass of said armature and said time delay mechanism being balanced on both sides f said pivot and means pivotally connected to said armaturefor sel-adjusting said mass as said armature moves said time delay mechanism for maintaining said balances 5. In combination, a magnet winding, a pivoted armature rotated about its pivot response to the energization of said magnet winding, and a time delay mechanism secured to Said armature on one side of its point of pivot, the mass of said armature and said time delay mechanism being balanced on both sides of said pivot, and a mass connected to the armature on the opposite side oi said pivot and connected to said time delay mechanism for adjusting the balancing force thereof as said time delay mechanism shifts its position in response to the armature movement.

6. In combination; a magnet, a pivoted armature rotatable about its pivot; a time delay mec'nanism connected to said armature on one side of its pivot; a weight connected to said armature 14 on the opposite side of said pivot from said time delay mechanism, and a link on which said Weight is pivotally mounted.

7. In combination; a magnet, a pivoted armature rotatable about its pivot; a time delay mechanism connected to said armature on one side of its pivot; a Weight connected to said armature on the opposite side of said pivot from said time delay .mechanism and a link on which said weight is pivotaliy mounted, said link and Weight being balanced against said time delay macina nism for all positions of said armature.

HERBERT C. GRAVES, Ja,

REFERENCES CITED yThe following references are of record ina the le of this patent:

UNITED STATES PATENTS Numbei` Name Data 570,212 Wurts Oct. 27, 1896 1,123,288 Hellmund Jan. 5, 1915 1,425,700 Scott Aug. 15, 1922 2,067,797 Smith Jan. 12, 193'? 2,134,951 Piesker Nov. i, 1933 2,165,037 Ellis et ai July 4, 1939 2,178,083 Sandin Oct. 31, 1939 1,652,550 Yeager Dec. 13, 1927 2,083,475 Ross June 3, 1937 2,088,174 Paullin July 27, 1937 

